alpha-Dystroglycan (DG) has been identified as the cellular receptor for lymphocytic choriomeningitis virus (LCMV) and Lassa fever virus (LFV). This subunit of DG is a highly versatile cell surface molecule that provides a molecular link between the extracellular matrix (ECM) and a beta-DG transmembrane component, which interacts with the actin-based cytoskeleton. In addition, DG exhibits a complex pattern of interaction with a wide variety of ECM and cellular proteins. In the present study, we characterized the binding of LCMV to alpha-DG and addressed the role of alpha-DG-associated host-derived proteins in virus infection. We found that the COOH-terminal region of alpha-DG's first globular domain and the NH2-terminal region of the mucin-related structures of alpha-DG together form the binding site for LCMV. The virus-alpha-DG binding unlike ECM alpha-DG interactions was not dependent on divalent cations. Despite such differences in binding, LCMV and laminin-1 use, in part, an overlapping binding site on alpha-DG, and the ability of an LCMV isolate to compete with laminin-1 for receptor binding is determined by its binding affinity to alpha-DG. This competition of the virus with ECM molecules for receptor binding likely explains the recently found correlation between the affinity of LCMV binding to alpha-DG, tissue tropism, and pathological potential. LCMV strains and variants with high binding affinity to alpha-DG but not low affinity binders are able to infect CD11c+ dendritic cells, which express alpha-DG at their surface. Infection followed by dysfunction of these antigen-presenting cells contributes to immunosuppression and persistent viral infection in vivo.